Strontium aluminate inorganic fibers

ABSTRACT

Inorganic fibers are disclosed, vacuum preforms of which have a shrinkage of 3.5% or less when exposed to 1260° C. for 24 hours. The fibers have a composition comprising SrO, Al 2  O 3 , and sufficient fiber forming additive to allow fiber formation but not so much as to increase shrinkage beyond 3.5%. A preferred range of fibers has a shrinkage of 3.5% or less when exposed to 1500° C. for 24 hours and may comprise (in weight percent): SrO 53.2%-57.6%, Al 2  O 3  30.4-40.1%, SiO 2  5.06-10.1%.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to man-made inorganic oxide fibres. The invention also relates to products formed from such fibres.

2. Description of the Related Art

Inorganic fibrous materials are well known and widely used for many purposes (e.g. as thermal or acoustic insulation in bulk, mat, or blanket form, as vacuum formed shapes, as vacuum formed boards and papers, and as ropes, yarns or textiles; as a reinforcing fibre for building materials; as a constituent of brake blocks for vehicles). In most of these applications the properties for which inorganic fibrous materials are used require resistance to heat, and often resistance to aggressive chemical environments.

Inorganic fibrous materials can be either glassy or crystalline. Asbestos is an inorganic fibrous material one form of which has been strongly implicated in respiratory disease.

It is still not clear what the causative mechanism is that relates some asbestos with disease but some researchers believe that the mechanism is mechanical and size related. Asbestos of a critical size can pierce cells in the body and so, through long and repeated cell injury, have a bad effect on health. Whether this mechanism is true or not regulatory agencies have indicated a desire to categorise any inorganic fibre product that has a respiratory fraction as hazardous, regardless of whether there is any evidence to support such categorisation. Unfortunately for many of the applications for which inorganic fibres are used, there are no realistic substitutes.

Accordingly there is a demand for inorganic fibres that will pose as little risk as possible (if any) and for which there are objective grounds to believe them safe.

One line of study has proposed that if inorganic fibres were made that were sufficiently soluble in physiological fluids that their residence time in the human body was short; then damage would not occur or at least be minimised. As the risk of asbestos linked disease appears to depend very much on the length of exposure this idea appears reasonable. Asbestos is extremely insoluble.

As intercellular fluid is saline in nature the importance of fibre solubility in saline solution has long been recognised. If fibres are soluble in physiological saline solution then, provided the dissolved components are not toxic, the fibres should be safer than fibres which are not so soluble. The shorter the time a fibre is resident in the body the less damage it can do.

Such fibres are exemplified by the applicant's earlier International Patent Applications WO93/15028 and WO94/15883 which disclose saline soluble fibres usable at temperatures of 1000° C. and 1260° C. respectively.

An alternative line of study has proposed that hydratable fibres that lose their fibrous nature in body fluids may offer another route to "safe" fibres in that the shape and size of the fibres may be what is causing damage. This route is exemplified by European Patent Application Nos. 0586797 and 0585547 which are aimed at providing silica free compositions and which disclose two calcium aluminate compositions (one containing 50/50 wt % alumina/calcined lime and the other disclosing 63/30 wt % alumina/calcined lime with additions of 5% CaSO₄ and 2% other oxides). Such fibres hydrate readily so losing their fibrous nature. Asbestos does not hydrate and seems to maintain its fibrous shape in body fluid effectively indefinitely.

SUMMARY OF THE INVENTION

The applicants have found that strontium aluminate compositions do not appear to form fibres when blown from a melt whereas such compositions including additives such as silica do form fibres when blown from a melt. Such fibres appear to hydrate in the manner of calcium aluminate fibres and additionally show the potential for high temperature use. Vacuum formed performs of some such fibres show shrinkages of 3.5% or less when exposed to 1260° C. for 24 hours; some show shrinkages of 3.5% or less when exposed to 1400° C. for 24 hours; and some even show shrinkages of 3.5% or less when exposed to 1500° C. for 24 hours. Such fibres provide a hydratable high temperature fibre usable in the products recited above.

Accordingly the present invention provides an inorganic fibre, a vacuum cast preform of which having a shrinkage of 3.5% or less when exposed to 1260° C. for 24 hours, the fibre comprising SrO, Al₂ O₃, and sufficient amount of a fibre forming additive to allow fibre formation, but not so much as to increase shrinkage beyond 3.5%.

Preferably the fibre forming additive comprises SiO₂ and the constituents SrO, Al₂ and SiO₂ comprise at least 90 wt % (more preferably at least 95 wt %) of the fibre composition.

Desirably, the inorganic fibres described above comprise SrO in an amount between 41.2 wt % and 63.8 wt % and Al₂ O₃ in an amount between 29.9 wt % and 53.1 wt %. These fibres can desirably contain an amount of SiO₂ greater than 2.76 wt % and less than 14.9 wt %.

Desirably, the amount of Al₂ O₃ in the fibres is 48.8 wt % or less. In addition, it is desirable that the weight percentage of SrO relative to the total amount of SrO plus Al₂ O₃ plus SiO₂ is greater than 53.7 wt % and less than 59.6 wt %. In an embodiment of the invention, the fibres comprise SrO in an amount of 53.2 wt % to 57.6 wt %, Al₂ O₃ in an amount of 30.4 wt % to 40.1 wt %, and SiO₂ in an amount of 5.06 wt % to 10.1 wt %, more particularly SrO in an amount of 53.2 wt % to 54.9 wt %, Al₂ O₃ in an amount of 39.9 wt % to 40.1 wt %, and SiO₂ in an amount of 5.06 wt % to 5.34 wt %.

DETAILED DESCRIPTION OF THE INVENTION

The scope of the invention is made clear in the appended claims with reference to the following description.

In the following, where reference is made to a saline soluble fibre, this is to be taken as meaning a fibre having a total solubility of greater than 10 ppm in saline solution as measured by the method described below, and preferably having much higher solubility.

The experiment results are described below with reference to Tables 1, 2, and 3.

Table 1 shows a series of compositions that were melted and blown in a conventional manner. Those compositions indicated as "&" did not form fibre to a useful extent but formed shot. For each of the compositions the analysed composition in weight percent (found from x-ray fluorescence analysis) is shown. Where a figure "<0.05" is shown this means that the component concerned could not be detected.

Owing to the nature of x-ray fluorescence measurements (which are sensitive to the surrounding environment) the total quantity of material found by analysis can add up to over 100% and in this patent specification (including the description claims and abstract) the figures have not been normalised to 100%. For each composition however the total quantity of analysed material is indicated and it can be seen that the variation from 100% is small. Under the column headed "Relative weight percent" the weight percentage of SrO, Al₂ O₃ and SiO₂ to the total of these components is indicated. Except where the context dictates otherwise any percentages quoted in this specification should be taken as percentages as analysed by x-ray fluorescence analysis and not absolute percentages.

Table 2 shows (in the same order as Table 1) shrinkage and solubility data for the fibre forming compositions. Solubility is expressed as parts per million in solution as measured in the method described below.

All of the compositions above and including line A of Tables 1 and 2 include 2.76 wt % or less SiO₂. It can be seen that most of these compositions did not form fibre. Some of the fibres include Na₂ O in amounts of 2.46 wt % or more to assist fibre forming but show poor shrinkage characteristics at temperatures above 1000° C. (in the sense of more than 3.5% at measured temperature).

One fibre (SA5(2.5% K20/SiO2)) which contains 1.96% K₂ O and 2.69% SiO₂ has acceptable shrinkage at 1260° C.

Thus it can be seen that "pure" strontium aluminates do not form fibres whereas by addition of fibre forming additives (e.g. SiO₂ and Na₂ O) fibres may be formed. The shrinkage characteristics of the resultant fibres depend upon the additives used.

The fibres below line A and above and including line B have a SrO content of less than 35 wt % and show poor shrinkage characteristics. The fibres shown below line B have a SrO content of greater than 35 wt % and where measured show acceptable shrinkage at 1260° C.

The fibre of line C comprises 2.52 wt % CaO and this appears to be damaging to performance at 1400° C. The fibres lying below line D and above and including line E have an Al₂ O₃ content of greater than 48.8 wt % which appears to affect adversely the performance of the fibres at 1400° C. The fibre below line E has a SiO₂ content of 14.9 wt % which appears to be bad for 1400° C. performance (see below for 1500° C. performance).

A further limited range of compositions (shown as bold text under the column 1400° C.) tend to have an acceptable shrinkage at 1400° C. These compositions lie below line C and above and including line D of Tables 1 & 2. The two fibres indicated in this range that do not meet the 3.5% shrinkage requirement may just be anomalous results.

The fibres lying below line C and above and including line D have been sorted on relative weight percent SrO (as defined above) and it can be seen that those compositions with a relative weight percent SrO of greater than 53.7% and less than 59.6% tend to have acceptable shrinkages at 1500° C. The fibre in this region that does not have acceptable shrinkage at 1500° C. is a high SiO₂ fibre (12.2 wt % SiO₂) and this supports the deleterious effect of too much SiO₂ mentioned above.

Two fibres (SA5a and SA5aII) show acceptable shrinkage at 1550° C.

Additionally it can be seen that some of the fibres show enormous solubilities and so may provide usable refractory fibres that will dissolve in body fluids.

All of the fibres showed hydration on insertion into aqueous fluids, indeed they tended to show some hydration on forming the preforms that were used for shrinkage testing. After 24 hours solubility testing in physiological-type fluids the hydration is very evident. The hydration takes the form of apparent dissolution and re-precipitation of crystals on the fibre surface that results in it losing its fibrous nature.

For some of the compositions, in making the vacuum preforms for testing a dispersant and wetting agent was used (Troy EX 516-2 (Trade mark of Troy Chemical Corporation)) which is a mixture of non-ionic surfactants and chemically modified fatty acids. This was in an attempt to minimise the time of exposure to water and hence the extent of hydration. It can be seen from Table 3 (which shows the same type of information as Table 2) that those compositions where the dispersant was used (indicated as "troy") tend to have a higher shrinkage than the identical composition not using the dispersant. The applicants surmise that this may be due to the partial hydration "locking" the fibres together so that any one fibre has to shrink against the tension of supporting fibres along its length: such tension may lead to fibre thinning rather than longitudinal shrinkage. When the dispersant is used the fibres are free to shrink along their length.

The following describes in detail the methods used to measure shrinkage and solubility.

Shrinkage was measure by proposed ISO standard ISO/TC33/SC2/N220 (equivalent to British Standard BS1920 part 6.1986) with some modifications to account for small sample size. The method in summary comprises the manufacture of vacuum cast preforms, using 75 g of fibre in 500 cm³ of 0.2% starch solution, into a 120×65 mm tool. Platinum pins (approximately 0. 5 mm diameter) were placed 100×45 mm apart in the 4 corners. The longest lengths (L1 & L2) and the diagonals (L3 & L4) were measured to an accuracy of ±5 μm using a travelling microscope. The samples were placed in a furnace and ramped to a temperature 50° C. below the test temperature at 300° C./hour and ramped at 120° C./hour for the last 50° C. to test temperature and left for 24 hours. The shrinkage values are given as an average of the 4 measurements.

It should be noted that although this is a standard way of measuring shrinkage of fibre it has an inherent variability in that the finished density of the preform may vary depending on casting conditions. Further it should be noted that fibre blanket will usually have a higher shrinkage than a preform made of the same fibre. Accordingly, the 3.5% figure mentioned in this specification is likely to translate as a higher shrinkage in finished blanket.

Solubility was measured by the following method.

The fibre was first chopped through a 10 mesh sieve and shot removed by hand sieving also through a 10 mesh sieve.

The solubility test apparatus comprised a shaking incubator water bath, and the test solution had the following composition:

    ______________________________________                                         Compound      Name             Grams                                           ______________________________________                                         NaCl          Sodium chloride  6.780                                             NH.sub.4 Cl Ammonium chloride 0.540                                            NaHCO.sub.3 Sodium bicarbonate 2.270                                           Na.sub.2 HPO.sub.4 H.sub.2 O Disodium hydrogen phosphate 0.170                 Na.sub.3 C.sub.6 H.sub.5 O.sub.7 · 2H.sub.2 O Sodium citrate                                       dihydrate 0.060                                   H.sub.2 NCH.sub.2 CO.sub.2H Glycine 0.450                                      H.sub.2 SO.sub.4 s.g. 1.84 Sulphuric acid 0.050                              ______________________________________                                    

The above materials were diluted to 1 litre with distilled water to form a physiological-like saline solution.

0.500 grams±0.003 grams of chopped fibre was weighed into a plastic centrifuge tube and 25 cm³ of the above saline solution added. The fibre and saline solution was shaken well and inserted into the shaking incubator water bath maintained at body temperature (37° C.±1° C.). The shaker speed was set at 20 cycles/minute.

After 24 hours the centrifuge tube was removed then supernatant liquid was decanted and the liquid passed through a filter (0.45 micron cellulose nitrate membrane filter paper [WCN type from Whatman Labsales Limited]) into a clean plastic bottle. The liquid was then analyzed by one of two methods. The first method used was atomic absorption using a Thermo Jarrell Ash Smith-Hiefje II machine.

The operating conditions were as set out in the applicant's earlier earlier International Patent Applications WO93/15028 and WO94/15883. For SrO the operating conditions were:

    ______________________________________                                         WAVELENGTH  BAND       CURRENT                                                   (nm) WIDTH (mA) FLAME                                                        ______________________________________                                         460.7       0          12        Fuel Lean                                     ______________________________________                                    

Strontium is measured against a standard atomic absorption solution (Aldrich 970 μm/ml). Three standards are prepared to which 0.1% KCI is added (Sr[ppm] 9.7,3.9 & 1.9). Dilutions of ×10 and ×20 are normally made to measure Sr level in the sample. SrO is then calculated as 1.183×Sr.

All stock solutions were stored in plastic bottles.

In the second method used (which was shown to give results consistent with the first method) element concentrations were found by inductively coupled plasma-atomic emission spectroscopy in known manner.

The above has discussed resistance to shrinkage of preforms exposed to 1260° C. for 24 hours. This is an indication of the maximum use temperature of a fibre. In practice fibres are quoted for a maximum continuous use temperature and a higher maximum exposure temperature. It is usual in industry when selecting a fibre for use at a given temperature to choose a fibre having a higher continuous use temperature than that normally required for the intended use. This is so that any accidental increase in temperature does not damage the fibres. It is quite usual for a margin of 100 to 150° C. to be given.

The applicants are not certain as yet as to how much other oxides or other impurities will affect the performance of fibres as described above and the appendant claims allow, where SiO₂ is the fibre forming additive, up to 10 wt % of materials other than SrO, Al₂ O₃ and SiO₂, although this should not be seen as limitative.

Although the above description has referred to manufacture of fibres by blowing from a melt the invention is not limited to blowing and also encompasses spinning and other techniques in which fibres are formed from a melt, and also encompasses fibres made by any other process.

                                      TABLE 1                                      __________________________________________________________________________                                                      Relative                         weight percent (to total                                                      Composition wt % SrO + Al.sub.2 O.sub.3 + SiO.sub.2)                         Comp  SrO                                                                               Al.sub.2 O.sub.3                                                                   SiO.sub.2                                                                         CaO                                                                               MgO                                                                               ZrO.sub.2                                                                         BaO                                                                               K.sub.2 O                                                                         Na.sub.2 O                                                                        P.sub.2 O.sub.5                                                                   Fe.sub.2 O.sub.3                                                                   Cr.sub.2 O.sub.3                                                                   Total                                                                              SrO Al.sub.2 O.sub.3                                                                   SiO.sub.2             __________________________________________________________________________     SA3 & 33.1                                                                              60.9                                                                               <0.05                                                                             0.08                                                                              <0.05                                                                             <0.05                                                                             0.20                                                                              <0.05                                                                             <0.05                                                                             0.06                                                                              1.92                                                                               <0.05                                                                              94.34                                                                              35.2%                                                                              64.8%                       SA1 & 61.4 37.1 <0.05 0.08 <0.05 <0.05 0.30 <0.05 <0.05 <0.05 <0.05                                                                       <0.05 98.58                                                                    62.3% 37.7%                                                                     SA2 & 48.5                                                                    49.7 <0.05                                                                     0.06 <0.05                                                                     <0.05 0.24                                                                     <0.05 <0.05                                                                    <0.05 0.64                                                                     <0.05 98.50                                                                    49.4% 50.6%                                                                     SA5 54.8                                                                      39.3 0.14                                                                      0.08 <0.05                                                                     <0.05 0.21                                                                     <0.05 5.14                                                                     <0.05 <0.05                                                                    <0.05 99.67                                                                    58.1% 41.7%                                                                    0.1%                                                                            (5% Na2O)                                                                      SA5 54.5                                                                      41.2 0.19                                                                      0.31 <0.05                                                                     <0.05 0.21                                                                     <0.05 2.46                                                                     <0.05 <0.05                                                                    <0.05 98.87                                                                    56.8% 43.0%                                                                    0.2%                                                                            (2.5%                                                                          Na2O)                                                                          SA5c & 50                                                                     39.4 2.51                                                                      0.08 3.29                                                                      <0.05 0.21                                                                     <0.05 <0.05                                                                    <0.05 1.07                                                                     <0.05 98.56                                                                    54.4% 42.9%                                                                    2.7%                                                                            SA8c & 24.1                                                                   72.9 2.52                                                                      0.06 <0.05                                                                     <0.05 0.10                                                                     <0.05 0.12                                                                     <0.05 <0.05                                                                    <0.05 99.80                                                                    24.2% 73.3%                                                                    2.5%                                                                            SA3c & 39.9                                                                   55.4 2.55                                                                      0.07 0.12                                                                      <0.05 0.19                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    <0.05 98.31                                                                    40.8% 56.6%                                                                    2.6%                                                                            SA5 56.4                                                                      38.8 2.57                                                                      0.20 0.08                                                                      <0.05 0.21                                                                     <0.05 2.57                                                                     <0.05 <0.05                                                                    <0.05 100.83                                                                   57.7% 39.7%                                                                    2.6%                                                                            (2.5% Na2O/        SiO2)                                                                          SA5 56.3 38.8 2.69 0.13 <0.05 <0.05 0.21 1.86 0.15 <0.05 0.36 <0.05                                                                       100.50 57.6%                                                                   39.7% 2.8%                                                                      (2.5% K2O/                                                                     SiO2)                                                                          SA9c & 44.5                                                                   52 2.71 0.07                                                                   <0.05 <0.05                                                                    0.17 <0.05                                                                     <0.05 <0.05                                                                    0.05 <0.05                                                                     99.50 44.9%                                                                    52.4% 2.7%                                                                      SA4c & 54.5                                                                   37.3 2.74                                                                      0.30 0.16                                                                      0.54 0.66                                                                      <0.05 0.22                                                                     <0.05 0.;08                                                                    <0.05 96.50                                                                    57.6% 39.5%                                                                    2.9%                                                                            SA2c & 48.1                                                                   47.1 2.76                                                                      0.08 <0.05                                                                     <0.05 0.22                                                                     <0.05 <0.05                                                                    <0.05 0.08                                                                     <0.05 98.34                                                                    49.1% 48.1%                                                                    2.8% A                                                                          SA8b 22.9                                                                     65.7 9.62                                                                      0.06 <0.05                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    <0.05 0.06                                                                     <0.05 98.28                                                                    23.3% 66.9%                                                                    9.8%                                                                            SA7b 26.2                                                                     62.4 9.62                                                                      0.10 <0.05                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    <0.05 0.08                                                                     <0.05 98.32                                                                    26.7% 63.5%                                                                    9.8%                                                                            SA7a 27.4                                                                     62.2 9.20                                                                      0.06 <0.05                                                                     0.06 0.16                                                                      <0.05 <0.05                                                                    <0.05 0.10                                                                     <0.05 99.18                                                                    27.7% 63.0%                                                                    9.3%                                                                            SA6b 32.9                                                                     56.1 9.43                                                                      0.06 <0.05                                                                     <0.05 0.16                                                                     <0.05 <0.05                                                                    <0.05 0.18                                                                     <0.05 98.65                                                                    33.4% 57.0%                                                                    9.6%                                                                            SA6d 32.9                                                                     58.8 7.09                                                                      0.07 <0.05                                                                     <0.05 0.11                                                                     <0.05 0.10                                                                     <0.05 <0.05                                                                    <0.05 99.07                                                                    33.3% 59.5%                                                                    7.2%                                                                            SA6a 33.6                                                                     59.5 5.12                                                                      0.08 0.14                                                                      <0.05 0.20                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    <0.05 98.64                                                                    34.2% 60.6%                                                                    5.2% B                                                                          SACS1 53.9                                                                    37.8 5.25                                                                      2.52 0.18                                                                      <0.05 0.23                                                                     <0.05 0.13                                                                     <0.05 <0.05                                                                    <0.05 100.01                                                                   55.6% 39.0%                                                                    5.4% C                                                                          SAR8 44.7                                                                     47.4 7.65                                                                      0.07 0.10                                                                      <0.05 0.19                                                                     <0.05 0.10                                                                     <0.05 <0.05                                                                    <0.05 100.20                                                                   44.8% 47.5%                                                                    7.7%                                                                            SAR5 45                                                                       44.9 9.77                                                                      0.06 <0.05                                                                     <0.05 0.17                                                                     <0.05 0.09                                                                     <0.05 <0.05                                                                    <0.05 100.00                                                                   45.1% 45.0%                                                                    9.8%                                                                            SAR9 47.5                                                                     45.4 5.30                                                                      0.24 0.11                                                                      <0.05 0.209                                                                    <0.05 0.19                                                                     <0.05 0.05                                                                     <0.05 99.00                                                                    48.4% 46.2%                                                                    5.4%                                                                            SA2a 48.9                                                                     44.8 4.72                                                                      0.08 <0.05                                                                     <0.05 0.24                                                                     <0.05 <0.05                                                                    <0.05 0.32                                                                     <0.05 99.06                                                                    49.7% 45.5%                                                                    4.8%                                                                            SAR4 50.5                                                                     39.8 9.85                                                                      0.07 <0.05                                                                     <0.05 0.18                                                                     <0.05 0.13                                                                     <0.05 <0.05                                                                    <0.05 100.50                                                                   50.4% 39.7%                                                                    9.8%                                                                            SAR7 50.8                                                                     42.3 7.41                                                                      0.07 0.05                                                                      <0.05 0.18                                                                     <0.05 0.13                                                                     <0.05 <0.05                                                                    <0.05 100.90                                                                   50.5% 42.1%                                                                    7.4%                                                                            SAR1 52.2                                                                     35.7 12.00                                                                     0.09 0.05                                                                      0.15 0.20                                                                      <0.05 0.12                                                                     <0.05 0.05                                                                     <0.05 100.60                                                                   52.3% 35.7%                                                                    12.0%                                                                           SA5d 53 39                                                                    7.63 0.10                                                                      0.12 <0.05                                                                     0.22 <0.05                                                                     0.23 <0.05                                                                     <0.05 <0.05                                                                    100.30 53.2%                                                                   39.1% 7.7%                                                                      SA5d II                                                                       54.2 39.6                                                                      7.57 0.08                                                                      0.08 <0.05                                                                     0.20 <0.05                                                                     0.23 <0.05                                                                     0.07 <0.05                                                                     101.96 53.5%                                                                   39.1% 7.5%                                                                      SA5b 52.3                                                                     35.1 10.00                                                                     0.10 0.12                                                                      <0.05 0.24                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    <0.05 97.86                                                                    53.7% 36.0%                                                                    10.3%                                                                           SA5a 53.2                                                                     39.9 5.34                                                                      0.14 <0.05                                                                     <0.05 0.26                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    <0.05 98.84                                                                    54.0% 40.5%                                                                    5.4%                                                                            SA5a II                                                                       54.9 40.1                                                                      5.06 0.08                                                                      <0.05 <0.05                                                                    0.26 <0.05                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    100.89 54.9%                                                                   40.1% 5.1%                                                                      SAR10 56.4                                                                    37.3 6.01                                                                      0.14 0.10                                                                      <0.05 0.21                                                                     <0.05 0.19                                                                     <0.05 0.07                                                                     <0.05 100.40                                                                   56.6% 37.4%                                                                    6.0%                                                                            SA4d 56.7                                                                     34.1 7.37                                                                      0.12 0.08                                                                      <0.05 0.22                                                                     <0.05 0.16                                                                     <0.05 0.06                                                                     <0.05 98.75                                                                    57.8% 34.7%                                                                    7.5%                                                                            SAR12 57.4                                                                    29.2 12.20                                                                     0.09 0.09                                                                      <0.05 0.23                                                                     <0.05 0.19                                                                     <0.05 <0.05                                                                    <0.05 99.40                                                                    58.1% 29.6%                                                                    12.3%                                                                           SA4b 57.6                                                                     30.4 10.10                                                                     0.08 <0.05                                                                     <0.05 0.30                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    <0.05 96.48                                                                    58.7% 31.0%                                                                    10.3%                                                                           SA4a 58.6                                                                     34.4 5.35                                                                      0.10 <0.05                                                                     <0.05 0.20                                                                     <0.05 <0.05                                                                    <0.05 0.18                                                                     <0.05 98.83                                                                    59.6% 35.0%                                                                    5.4%                                                                            SAR3 61.3                                                                     29.9 9.73                                                                      0.09 <0.05                                                                     <0.05 0.23                                                                     <0.05 0.10                                                                     <0.05 <0.05                                                                    <0.05 101.40                                                                   60.7% 29.6%                                                                    9.6%                                                                            SAR6 61.7                                                                     32.4 7.44                                                                      0.08 <0.05                                                                     <0.05 0.22                                                                     <0.05 0.11                                                                     <0.05 <0.05                                                                    <0.05 102.00                                                                   60.8% 31.9%                                                                    7.3%                                                                            SA1a 63.8                                                                     29.9 4.84                                                                      0.08 <0.05                                                                     <0.05 0.30                                                                     <0.05 <0.05                                                                    0.08 0.18                                                                      0.06 99.22                                                                     64.7% 30.3%                                                                    4.9% D                                                                          SA9a 44                                                                       48.9 4.95                                                                      0.07 <0.05                                                                     <0.05 0.21                                                                     <0.05 <0.05                                                                    <0.05 <0.05                                                                    <0.05 98.13                                                                    45.0% 50.0%                                                                    5.1%                                                                            SA3a 41.2                                                                     53.1 4.74                                                                      0.06 <0.05                                                                     <0.05 0.22                                                                     <0.05 <0.05                                                                    <0.05 0.06                                                                     <0.05 99.38                                                                    41.6% 53.6%                                                                    4.8% E                                                                          SAR2 54.9                                                                     30.6 14.90                                                                     0.08 0.05                                                                      0.08 0.19                                                                      <0.05 0.10                                                                     <0.05 <0.05                                                                    <0.05 100.90                                                                   54.7% 30.5%                                                                    14.8%             __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________                                         Relative weight                              Shrinkage at 24 hours percent (to total Solubility                             (° C.) SrO + Al.sub.2 O.sub.3 + SiO.sub.2) ppm                        Comp     1000                                                                              1200                                                                              1260                                                                              1350                                                                              1400                                                                              1450                                                                              1500                                                                              1550                                                                              1600                                                                              SrO Al.sub.2 O.sub.3                                                                   SiO.sub.2                                                                          SrO                                                                               Al.sub.2 O.sub.3                                                                   SiO.sub.2                                                                         Total                __________________________________________________________________________     SA3 &                               35.2%                                                                              64.8%                                    SA1 &          62.3% 37.7%                                                     SA2 &          49.4% 50.6%                                                     SA5 (5% Na2O)      8.22    58.1% 41.7% 0.1% 65 1000 1 1066                     SA5 (2.5% Na2O) 3.38  8.64       56.8% 43.0% 0.2% 1 563 1 565                  SA5c &          54.4% 42.9% 2.7%                                               SA8c &          24.2% 73.3% 2.5%                                               SA3c &          40.8% 56.6% 2.6%                                               SA5 (2.5% Na2O/ 2.39 3.95 6.53       57.7% 39.7% 2.6% 10 500 1 511                                                                         SiO2)                                                                          SA5(2.5%                                                                      K2O/   3.02                                                                         57.6%                                                                     39.7% 2.8%                                                                     11  2 13                                                                        SiO2)                                                                          SA9c &                                                                            44.9%                                                                      52.4% 2.7%                                                                      SA4c &                                                                            57.6%                                                                      39.5% 2.9%                                                                      SA2c &                                                                            49.1%                                                                      48.1% 2.8%                                                                      SA8b 10.16                                                                    12.1                                                                           23.3% 66.9%                                                                    9.8% 5 2 3                                                                     10                  SA7b 4.82  5.33       26.7% 63.5% 9.8%                                         SA7a 4.4  5.4   9.94    27.7% 63.0% 9.3% 4 2 2 8                               SA6b 3.62  6.42       33.4% 57.0% 9.6% 5 1 1 7                                 SA6d   7.48  7.8     33.3% 59.5% 7.2% 4 1 1 6                                  SA6a 7.02  8.81   6.52    34.2% 60.6% 5.2% 8 2 3 13 B                          SACS1   2.15  4.8     55.6% 39.0% 5.4% 26 1 2 29 C                             SAR8  0.94   1.14 7.86 39.6   44.8% 47.5% 7.7% 6   6                           SAR5  1.55   1.61 1.70 33.6   45.1% 45.0% 9.8% 8 2 1 11                        SAR9 1.25 2.52 2.85 3.77 5.91     48.4% 46.2% 5.4% 10  10 20                   SA2a   1.61  2.67 7.75    49.7% 45.5% 4.8% 10 1 6 17                           SAR4  1.06   1.6 3.19 31.1   50.4% 39.7% 9.8% 6   6                            SAR7  1.07  2.26 2.94 4.7    50.5% 42.1% 7.4% 7   7                            SAR1 0.75 1.10 1.19 1.36 2.14 25.25    52.3% 35.7% 12.0% 14  1 15                                                                          SA5d                                                                          1.36  4.21                                                                     53.2% 39.1%                                                                    7.7% 17 1 1                                                                    19                  SA5d II     1.3  4.13   53.5% 39.1% 7.5%                                       SA5b 0.6  0.69  0.66 2.6 4.7   53.7% 36.0% 10.3% 11  3 14                      SA5a   0.89  1.1  1.78 3.19 5.88 54.0% 40.5% 5.4% 45  2 47                     SA5a II     2.71 2.75 2.86 3.14 9.46 54.9% 40.1% 5.1%                          SAR10 2.18 2.2 2.23  2.48  2.51 Melts  56.6% 37.4% 6.0% 56  7 63                                                                           SA4d                                                                          1.69 2.77                                                                      3.36  6.9                                                                      57.8% 34.7%                                                                    7.5% 15 1 2                                                                    18                  SAR12  1.4 1.4  1.31  Melts   58.1% 29.6% 12.3% 25  2 27                       SA4b 0.55  0.41  1.19 1.16 1.93   58.7% 31.0% 10.3% 15  3 18                   SA4a   1.56  4.6     59.6% 35.0% 5.4% 19 1 2 22                                SAR3  1.49 1.35 1.98 2.21 5.31    60.7% 29.6% 9.6% 22  2 24                    SAR6  1.42   2.22 2.42 6.36 8.19  60.8% 31.9% 7.3% 15   15                     SA1a   2.37   8.57    64.7% 30.3% 4.9% 161 897 4 1062 D                        SA9a     7.19     45.0% 50.0% 5.1% 5 1 1 7                                     SA3a 1.12  2.45 3.94 6.43     41.6% 53.6% 4.8% 12 3 6 21 E                     SAR2  0.73 2.00 3.94 8.43     54.7% 30.5% 14.8% 14  2 16                     __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________               Shrinkage at 24 hours      Relative weight percent                     (° C.) (to total SrO + Al.sub.2 O.sub.3 + SiO.sub.2) Solubility       Comp      1000                                                                              1200                                                                              1260                                                                              1350                                                                              1400                                                                              1450                                                                              1500                                                                              1550                                                                              1600                                                                              SrO Al.sub.2 O.sub.3                                                                    SiO.sub.2                                                                          SrO                                                                               Al.sub.2 O.sub.3                                                                   SiO.sub.2                                                                         Total              __________________________________________________________________________     SA4d                  1.69                                                                              2.77                                                                              3.36  6.9                                                                               57.8%                                                                              34.7%                                                                               7.5%                                                                               13 1   1  5                    SA4d (troy)     3.12 3.86 4.72  13.62 57.8% 34.7% 7.5%                         SA5a II     2.71 2.75 2.86 3.14  54.9% 40.1% 5.1%                              SA5a II-troy     1.56    14.2 54.9% 40.1% 5.1%                                 SA5d     1.36  4.21   53.2% 39.1% 7.7% 17 1 1 19                               SA5d (troy)     0.93  6.04   53.2% 39.1% 7.7%                                  SA5d II     1.3  4.13   53.5% 39.1% 7.5%                                       SA5d II (troy)     1.35  5.21   53.5% 39.1% 7.5%                               SA5 (2.5% Na2O/ 2.39 3.95 6.53       57.8% 39.7% 2.6%                          SiO2)                                                                          SA5 (2.5% Na2O/   7.17       57.7% 39.7% 2.6%                                  SiO2) troy                                                                     SA5 (5% Na2O)      8.22    58.1% 41.7% 0.1% 50 1200 1 125                      SA5 (5% Na2O) troy      14.47    58.1% 41.7% 0.1%                              SA6b 3.62  6.42       33.4% 57.0% 9.6% 7 2 2 11                                SA6b (troy)   13.18       33.4% 57.0% 9.6%                                   __________________________________________________________________________ 

I claim:
 1. An inorganic fibre, a vacuum preform of which has a shrinkage of 3.5% or less when exposed to a temperature of 1260° C. for 24 hours, the fibre having a strontium aluminate composition comprising SrO in an amount of 35 wt % or greater based upon the total fibre composition, Al₂ O₃, and an amount of fibre forming additive effective to allow fibre formation, the amount of said fibre forming additive being not so great as to increase shrinkage beyond 3.5%, and in which, when SiO₂ is present, the amount of SiO₂ is less than 14.9 wt % based upon the total fiber composition.
 2. An inorganic fibre as claimed in claim 1, in which the fibre forming additive comprises SiO₂ and the constituents SrO, Al₂ O₃ and SiO₂ comprise at least 90 wt % of the fibre composition.
 3. An inorganic fibre as claimed in claim 2 in which the constituents SrO, Al₂ O₃ and SiO₂ comprise at least 95 wt % of the fibre composition.
 4. An inorganic fibre as claimed in claim 1, a vacuum preform of which has a shrinkage of 3.5% or less when exposed to 1400° C. for 24 hours.
 5. An inorganic fibre as claimed in claim 1, wherein the amount of Al₂ O₃ is 48.8 wt % or less.
 6. An inorganic fibre as claimed in claim 1, a vacuum preform of which has a shrinkage of 3.5% or less when exposed to 1500° C. for 24 hours.
 7. An inorganic fibre as claimed in claim 5, wherein the weight percentage of SrO calculated based upon the total of the amount of SrO plus the amount of Al₂ O₃ plus the amount of SiO₂ is in the range greater than 53.7 wt % to less than 59.6 wt %.
 8. An inorganic fibre as claimed in claim 1 in which the fibre forming additive comprises Na₂ O in an amount less than 2.46 wt %.
 9. An inorganic fibre as claimed in claim 1, a vacuum preform of which has a shrinkage of 3.5% or less when exposed to 1550° C. for 24 hours.
 10. An inorganic fibre, a vacuum preform of which has a shrinkage of 3.5% or less when exposed to 1260° C. for 24 hours, the fibre having a strontium aluminate composition comprising

    ______________________________________                                         SrO              41.2 wt %-63.8 wt %;                                            Al.sub.2 O.sub.3 29.9 wt %-53.1 wt %;                                        ______________________________________                                    

and an amount of fibre forming additive effective to allow fibre formation, the amount of said fibre forming additive being not so great as to increase shrinkage beyond 3.5%.
 11. An inorganic fibre, a vacuum preform of which has a shrinkage of 3.5% or less when exposed to 1260° C. for 24 hours, the fibre having a strontium aluminate composition comprising:

    ______________________________________                                         SrO      41.2 wt %-63.8 wt %                                                     Al.sub.2 O.sub.3 29.9 wt %-53.1 wt % and                                       SiO.sub.2 2.76 wt %-14.9 wt % as a fibre                                        forming additive effective to allow fibre formation.                        ______________________________________                                    


12. The inorganic fiber according to claim 11, wherein the combined weight of SrO, Al₂ O₃, and SiO₂ is at least 90 wt % of the fiber composition.
 13. The inorganic fiber according to claim 12, wherein the combined weight of SrO, Al₂ O₃, and SiO₂ is at least 95 wt % of the fiber composition.
 14. The inorganic fiber according to claim 12, comprising in wt % based upon the total weight of fiber composition:

    ______________________________________                                         SrO              53.2 wt %-57.6 wt %;                                            Al.sub.2 O.sub.3 30.4 wt %-40.1 wt %;                                          SiO.sub.2 5.06 wt %-10.1 wt %. - - -                                         ______________________________________                                    


15. The inorganic fiber according to claim 12, comprising in wt % based upon the total weight of fiber composition:

    ______________________________________                                         SrO              53.2 wt %-54.9 wt %;                                            Al.sub.2 O.sub.3 39.9 wt %-40.1 wt %;                                          SiO.sub.2 5.06 wt %-5.34 wt %;                                               ______________________________________                                    


16. An inorganic fibre a vacuum preform of which has a shrinkage of 3.5% or less when exposed to 1260° C. for 24 hours and a shrinkage of 3.5% or less when exposed to 1500° C. for 24 hours, the fibre having a strontium aluminate composition comprising in wt %:

    ______________________________________                                         SrO              53.2 wt %-57.6 wt %;                                            Al.sub.2 O.sub.3 30.4 wt %-40.1 wt %;                                          SiO.sub.2 5.06 wt %-10.1 wt %;                                               ______________________________________                                    

and wherein the weight percentage of SrO relative to the total amount of SrO plus Al₂ O₃ plus SiO₂ is in the range greater than 53.7 wt % to less than 59.6 wt %.
 17. An inorganic fibre a vacuum preform of which has a shrinkage of 3.5% or less when exposed to 1260° C. for 24 hours and a shrinkage of 3.5% or less when exposed to 1500° C. for 24 hours, the fibre having a strontium aluminate composition, calculated based upon the total fiber composition comprising:

    ______________________________________                                         SrO              53.2 wt %-54.9 wt %;                                            Al.sub.2 O.sub.3 39.9 wt %-40.1 wt %;                                          SiO.sub.2 5.06 wt %-5.34 wt %;                                               ______________________________________                                    

and wherein the weight percentage of SrO calculated based upon the total of the amount of SrO plus the amount of Al₂ O₃ plus the amount of SiO₂ is in the range greater than 53.7 wt % to less than 59.6 wt %.
 18. A process for the formation of fibres from a melt comprising predominantly SrO and Al₂ O₃, the process comprising the steps of (1) adding minor amounts of SiO₂ to the melt to allow fibre formation, the constituents SrO, Al₂ O₃, and SiO₂ comprising at least 90 wt % of the melt and SiO₂ comprising less than 14.9 wt % of the melt, and (2) forming at least one fibre from the melt.
 19. Thermal insulation in a form selected from the group consisting of bulk, mat, blanket, vacuum formed shapes, boards, and papers, ropes, yarns, and textiles, comprising an inorganic fiber, a vacuum preform of which has a shrinkage of 3.5% or less when exposed to 1260° C. for 24 hours, the fiber having a strontium aluminate composition comprising SrO in an amount of 35 wt % or greater, Al₂ O₃, and an amount of fiber forming additive effective to allow fiber formation,the amount of said fiber forming additive being not so great as to increase shrinkage of the vacuum preform above 3.5%, and wherein, when SiO₂ is present in the inorganic fiber, the amount of SiO₂ is less than 14.9 wt %.
 20. An inorganic fiber comprising SrO, Al₂ O₃, and SiO₂, comprising amounts thereof in wt % based upon the weight of the total fiber composition, selected from the group consisting of:

    ______________________________________                                         SrO           Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                ______________________________________                                         41.2          53.1    4.74                                                       44.7 47.4 7.65                                                                 45.0 44.9 9.77                                                                 47.5 45.4 5.30                                                                 48.9 44.8 4.72                                                                 50.5 39.8 9.85                                                                 50.8 42.3 7.41                                                                 52.2 35.7 12.00                                                                52.3 35.1 10.00                                                                53.0 39.0 7.63                                                                 53.2 39.9 5.34                                                                 53.9 37.8 5.25                                                                 54.2 39.6 7.57                                                                 54.9 40.1 5.06                                                                 54.9 30.6 14.90                                                                56.3 38.8 2.69                                                                 56.4 37.3 6.01                                                                 56.7 34.1 7.37                                                                 57.4 29.2 12.20                                                                57.6 30.4 10.10                                                                58.6 34.4 5.35                                                                 61.3 29.9 9.73                                                                 61.7 32.4 7.44                                                                   and                                                                          63.8 29.9 4.84. - - -                                                        ______________________________________                                    


21. An inorganic fiber comprising SrO, Al₂ O₃, and SiO₂, comprising in wt % based upon the total weight of the fiber composition:

    ______________________________________                                                SrO          41.2 to 63.8;                                                Al.sub.2 O.sub.3 29.2 to 53.1;                                                 SiO.sub.2 2.69 to 14.9;                                                      ______________________________________                                    


22. An inorganic fiber comprising SrO, Al₂ O₃, and SiO₂, comprising amounts thereof in wt % based upon the weight of the total fiber composition, selected from the group consisting of:

    ______________________________________                                         SrO           Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                ______________________________________                                         53.9          37.8    5.25                                                       47.5 45.4 5.30                                                                 58.6 34.4 5.35                                                                 63.8 29.9 4.84                                                                 41.2 53.1 4.74                                                                   and                                                                          54.9 30.6 14.9. - - -                                                        ______________________________________                                    


23. An inorganic fiber comprising SrO, Al₂ O₃, and SiO₂, comprising amounts thereof in wt % based upon the weight of the total fiber composition, selected from the group consisting of:

    ______________________________________                                         SrO           Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                ______________________________________                                         44.7          47.4    7.65                                                       45.0 44.9 9.77                                                                 48.9 44.8 4.72                                                                 50.5 3.98 8.85                                                                 50.8 42.3 7.41                                                                 52.2 35.7 12.00                                                                52.3 35.1 10.00                                                                53.0 39.0 7.63                                                                 53.2 39.9 5.34                                                                 54.2 39.6 7.57                                                                 54.9 40.1 5.06                                                                 56.3 38.8 2.69                                                                 56.4 37.3 6.01                                                                 56.7 34.1 7.37                                                                 57.4 29.2 12.20                                                                57.6 30.4 10.10                                                                61.3 29.9 9.73                                                                   and                                                                          61.7 32.4 7.44. - - -                                                        ______________________________________                                     